For values of pow other than
0 , this term adds one network statistic to the model,
equaling the sum, over directed edges \((i,j)\) , of
sign.action(attr[i]-attr[j])^pow if dir is
"t-h" and of sign.action(attr[j]-attr[i])^pow if
"h-t" . That is, the
argument dir determines which vertex's attribute is
subtracted from which, with tail being the origin of a directed edge
and head being its destination, and bipartite networks' edges being
treated as going from the first part (b1) to the second (b2).
If pow==0 , the exponentiation is replaced by the signum
function: +1 if the difference is positive, 0 if there
is no difference, and -1 if the difference is negative. Note
that this function is applied after the
sign.action . The comparison is exact, so when using
calculated values of attr , ensure that values that you
want to be considered equal are, in fact, equal.
# binary: diff(attr, pow=1, dir="t-h", sign.action="identity")# valued: diff(attr, pow=1, dir="t-h", sign.action="identity", form ="sum")
a vertex attribute specification (see Specifying Vertex attributes and Levels (?nodal_attributes) for details.)
exponent for the node difference
determines which vertix's attribute is subtracted from which. Accepts: "t-h" (the default), "tail-head" , "b1-b2", "h-t" , "head-tail" , and "b2-b1" .
one of "identity", "abs", "posonly", "negonly". The following sign.actions are possible:
"identity" (the default) no transformation of the
difference regardless of sign
"abs" absolute value of the difference: equivalent
to the absdiff term
"posonly" positive differences are kept, negative
differences are replaced by 0
"negonly" negative differences are kept, positive
differences are replaced by 0
character how to aggregate tie values in a valued ERGM
ergmTerm for index of model terms currently visible to the package.
ergm:::.formatTermKeywords("ergmTerm", "diff", "subsection")